1. Field of the Invention
The present invention relates to a fuel cell including an electrolyte electrode assembly interposed between a pair of separators. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte interposed between the electrodes. A reactant gas supply passage and a reactant gas discharge passage extend through the separators in a stacking direction. A reactant gas flow field is connected between the reactant gas supply passage and the reactant gas discharge passage, and supplies a reactant gas to the electrode.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which comprises two electrodes (anode and cathode) and an electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is interposed between separators. The membrane electrode assembly and the separators make up a unit of the fuel cell for generating electricity. A predetermined number of fuel cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas such as a hydrogen-containing gas is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions (protons) and electrons. The hydrogen ions move toward the cathode through the electrolyte, and the electrons flow through an external circuit to the cathode, creating a DC electric current. An oxygen-containing gas or air is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen to produce water.
In the fuel cell, it is desirable to improve the sealing characteristics of the membrane electrode assembly and the separators. For example, Japanese laid-open patent publication No. 2001-319667 discloses a fuel cell directed to improve the sealing characteristics. As shown in FIG. 7, the fuel cell includes a membrane electrode assembly 1, and first and second separators 2, 3. The membrane electrode assembly 1 includes an anode 5, and a cathode 6, and a solid polymer electrolyte membrane 4 interposed between the anode 5 and the cathode 6. The anode 5 includes a gas diffusion layer 5a and an electrode catalyst layer 5b. The cathode 6 includes a gas diffusion layer 6a and an electrode catalyst layer 6b. The solid polymer electrolyte membrane 4 has an extension extending outwardly from the cathode 5 and the anode 6. The first and second separators 2, 3 have grooves 2a, 3a, respectively, at a position corresponding to the extension of the solid polymer electrolyte membrane 4. Liquid seals 7 are provided in the grooves 2a, 3a, respectively. The liquid seals 7 are made of a heat curing fluoride or silicone. The liquid seals 7 are applied in the grooves 2a, 3a in a liquid state. In the liquid state, the liquid seals 7 have a certain viscosity. In use, the liquid seals 7 are hardened to have a certain elasticity in a solid state. The liquid seals 7 are tightly in contact with the extension of the solid polymer electrolyte membrane 4, and end surfaces of the gas diffusion layers 5a, 6a, and the electrode catalyst layers 5b, 6b. 
However, it is difficult to ensure that the liquid seals 7 provided around the cathode 5 and the anode 6 are tightly in contact with the end surfaces of the gas diffusion layers 5a, 6a, and the electrode catalyst layers 5b, 6b due to the factor such as the tolerance in producing, and assembling the components. If there is a clearance between the liquid seals 7 and the gas diffusion layers 5a, 6a, the reactant gas may leak into the clearance. Some of the reactant gas such as an oxygen-gas and a fuel gas leaks into the reactant gas discharge passage through the clearance, and is not supplied to electrode surfaces of the cathode 5 and the anode 6. Consequently, the power generation can not be performed efficiently.
Though not illustrated, a coolant for cooling the electrode surface may also leak into a coolant flow field through the clearance around the electrode surface. Since the coolant does not flow along the electrode surface, the electrode surface is not cooled by the coolant efficiently.